Prostomium
From Wikipedia, the free encyclopedia
Prostomium (sometimes also called acron) is the first body segment in annelids worms. It is in front of (but does not include) the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth. It sometimes bears antennae and eyes. By feeding, it often functions like a kind of overlip. The shape and composition of prostomium are important for annelid systematics.
The prostomium often also has appendages such as palps and tentacles or cirri. Some polychaetes have a posterior extension with sensory function on it, called caruncle. A ciliated pit or groove at the posterior end of the prostomium is another kind or sensory organ called nuchal organ (or a variety of it, the nuchal epaulette).
